Anionic polymerization of conjugated dienes with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references including U.S. Pat. No. Re. 27,145 which teaches a relationship between the amount of 1,2-addition of butadiene and the glass transition temperatures of the hydrogenated butadiene polymers.
The capping of living anionic polymers to form functional end groups is described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of particular interest for the present invention are anionic polymers that are capped on one or more ends with hydroxyl, carboxyl, phenol, epoxy, and amine groups.
Anionic polymerization using protected functional initiators having the structure R.sup.1 R.sup.2 R.sup.3 Si--O--A'--Li is described in WO 91/12277 wherein R.sup.1, R.sup.2, and R.sup.3 are preferably alkyl, alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A' is preferably a branched or straight chain bridging group having at least 2 carbon atoms. The bridging group is most preferably a straight chain alkyl having from 3 to 10 carbon atoms and is exemplified by the following compound: ##STR1## which is readily prepared by lithiation of the reaction product of 1-chloro-6-hydroxy-n-hexane and t-butyldimethylchlorosilane. The use of such an initiator as Structure (1) to polymerize the desired monomer(s), followed by capping to produce the second terminal alcohol group, has several advantages over the preparation of telechelic diols by capping polymers prepared with difunctional initiators such as 1,4 dilithiobutane and lithium naphthalide. In addition to providing the option of polymerizing in non-polar solvents, this route avoids the formation of ionic gels, which are known to occur when diinitiated polymers are capped with reagents such as ethylene oxide, generating the polymeric di-alkoxide. These gels form even in relatively polar solvent mixtures and greatly complicate subsequent processing steps. By capping to produce the alkoxide on only one polymer terminus, these gels are avoided.
The initiator of Structure (1) anionically polymerizes unsaturated monomers like conventional lithium initiators but starts the polymer chain with a t-butyldimethylsiloxy functional group that can be readily converted to a primary alcohol, which is useful in a variety of subsequent reactions. While it appears that the majority of Structure (1) is active if the initiation step is performed at a low temperature (-5.degree. C.), at slightly higher temperatures, a significant fraction of the initiator charge fails to initiate polymerization; a large portion of the initiator is non-reactive or "dead". Initiation with sec-butyllithium occurs efficiently well above room temperature. Nevertheless, the active portion of the initiator of Structure (1) produces living polymers that can be further endcapped and hydrogenated like conventional anionic polymers.
It is an object of the present invention to provide improved protected functional initiators that operate efficiently (with a minimum of dead initiator) at economical temperatures . It is also an object of this invention to make functionalized anionic polymers having terminal functional groups on one or more ends of the polymer molecules.